This invention relates to high-power semiconductor switching power regulators such as are used in propulsion systems of diesel-electric locomotives and, more particularly, to a method and apparatus which provide low inductance, sufficient cooling capacity and easy installation and maintenance of insulated gate bipolar transistors (IGBTs) in such power regulators.
Traction vehicles such as, for example, locomotives, employ electric traction motors for driving wheels of the vehicles. In some of these vehicles, the motors are alternating current (AC) motors whose speed and power are controlled by varying the frequency and current of AC electric power supplied to the motors. Commonly, the electric power is supplied at some point in the vehicle system as direct current power and is thereafter inverted to AC power of controlled frequency and amplitude. The electric power may be derived from an on-board alternator driven by an internal combustion engine or may be obtained from a wayside power source such as a third rail or overhead catenary.
In conventional systems the power is inverted in a solid-state inverter incorporating a plurality of diodes and electronic switching devices. In a locomotive, large off-highway vehicle, or transit application, the traction motors may develop more than 1000 horsepower per motor thus requiring very high power handling capability by the associated inverter. This, in turn, requires semiconductor switching devices such as GTOs (gate turn-off thyristors) or IGBTs which are capable of controlling such high power and of dissipating significant heat developed in the semiconductor devices due to internal loss generating characteristics.
The semiconductor devices are mounted on heat transfer devices such as heat sinks which aid in transferring heat away from the semiconductor devices and thus preventing thermal failure of the devices. For these very high power semiconductors it is desirable to use heat sinks having generally hollow interiors through which cooling air can be forced to remove heat. An electrical circuit area in which the semiconductors are located may include the various control and timing circuits, including low power semiconductors, used in controlling switching of the power semiconductors.
In locomotive applications, an inverter for large AC motor applications typically includes six high power GTO or IGBT devices requiring heat sinks and forced air cooling. If IGBTs are used, each of these devices are generally power modules which require one sided cooling. A common arrangement thus requires six heat sinks per inverter. On a six axle locomotive, the inverters will include 36 heat sinks requiring cooling air.
Commonly assigned R. B. Bailey et al., "High Power Inverter Air Cooling", U.S. application Ser. No. 08/839,113, filed Apr. 23, 1997, describes a power converter system for an electric traction motor vehicle in which a plurality of high power IGBT devices are connected in circuit with at least one electric traction motor for controlling electric power to the motor. The IGBT devices are each thermally mounted on generally flat plate heat sinks having a plurality of fins extending therefrom and adapted for passing cooling air therethrough for extracting heat from the devices. The fins may be attached directly to the module heat sink or attached to a separate thermally conductive plate which is thermally bonded to the heat sink. Each of the heat sinks are mounted to a common air plenum forming one wall of an electrical circuit area of the vehicle. Cooling air is directed through the fins and out through an exhaust conduit. The system operates most efficiently if the inductance between the IGBTs and the DC link capacitor is minimized.
A conventional design for low to medium power inverters may include a single five layer bus structure for all three phases which interconnects six IGBT modules and several DC link capacitors. In the event of a failure in an IGBT module, the entire inverter must be removed. For repair, the bus bar must be disconnected from all six IGBT modules and the DC link capacitors before a failed IGBT module can be replaced.
For higher power applications, a single phase assembly generally includes two IGBT and heat sink modules and a DC link capacitor. The IGBT collector of one module is connected to the positive DC bus, the emitter of the IGBT module is connected to the collector of the other IGBT module to form the AC connection point, and the emitter of the other IGBT module is connected to the negative DC bus. An additional bus bar is used to connect bus bars of three of the single phase assemblies to provide three phase power. In the event of an IGBT failure, the pair of IGBT and heat sink modules and typically the local DC link capacitor need to be removed. Although a single phase assembly is removable without removing the other the phases, the removable section remains larger and heavier than desired.
Commonly assigned R. B. Bailey, U.S. Pat. No. 5,253,613 describes a GTO based inverter in which failed GTOs can be removed and replaced without having to remove any other hardware. In conventional IGBT systems, single IGBT/heat sink combinations are not easily replaced.